Saturdays tragic incident along the Afghan-Pakistan border, and its response, are familiar to any observer of Afghan-Pakistan-United States ties over the past decade. Nato aircraft highly likely in the words of an alliance spokesperson killed 24 Pakistani troops and wounded 13 others at two posts located about 1,000 feet apart on a mountain in the Mohmand region of Pakistans Federally Administered Tribal Areas (FATA). In response to the pre-dawn attack, which found most of the garrison still asleep, Pakistani authorities have again blocked vital supply routes for the Nato-led International Security Assistance Force (ISAF) in Afghanistan. The government also said it would review all diplomatic, military and intelligence cooperation with ISAF forces. Pakistani authorities also repeated their demand that the Pentagon leave the Shamsi Air Base in Balochistan Province used to service US drones that launch missiles at al-Qaeda and Taliban militants in Pakistans tribal region. This time they included a 15-day deadline for the withdrawal. A spokesman for Nato forces, Brig Gen Carsten Jacobson, said Afghan and ISAF troops were operating in the border area of eastern Afghanistan when a tactical situation prompted them to call in airstrikes in support that highly likely caused Pakistani casualties. Ironically, the airstrike came one day after a meeting between Gen John Allen, in charge of ISAF, and Pakistan Army Chief Gen Ashfaq Parvez Kayani in Islamabad to review border operations. According to a Pakistani military statement, the two discussed coordination, communication and proceduresaimed at enhancing border control on both sides. This is only the latest crisis to befall the border region during the last decade. Relations among Afghanistan, Pakistan, and the United States have been extraordinarily troubled for most of the past ten years. Historical conflicts, different priorities, and personal animosities have combined to weaken the collective ability of the three countries to repress extremists operating along the Afghanistan-Pakistan border region. The United States has pursued several initiatives to reduce tensions between Afghanistan and Pakistan and to encourage both governments to concentrate their attention on countering the Taliban and al-Qaeda terrorists operating inside their territories. Despite these efforts, the border region remains a major source of tension in their trilateral relationship. Most recently, the intensified fighting in Afghanistan has prompted ISAF to adopt a more aggressive policy along the frontier. Hence, Saturdays incident was bound to happen someday. For some time, the US helicopters assigned to ISAF have been engaging in a more aggressive campaign to defend Afghan border outposts. Taliban and Haqqani network guerrillas sally forth from their sanctuaries and attack Afghan army outposts in eastern Afghanistan. ISAF commanders had been justifying the border air strikes by citing the allegedly failure of the Pakistani Army to occupy and suppress the guerrilla and terrorist bases in the tribal regions, especially in North Waziristan. The White House and the Pentagon have become increasingly frustrated by the presence of the 'insurgent sanctuaries on Pakistani territory and the failure of the Pakistani government to establish control there. The Obama administration has authorised a more proactive air campaign against these militants. While still declining to send US ground forces across the border into Pakistan, the Pentagon has increased the use of both manned helicopter attacks along the border and unmanned aerial vehicle strikes for striking targets deeper inside Pakistani territory. A similar incident happened in September 2010, when US helicopters under ISAF attacked a Pakistan border post and killed two members of the Frontier Corps who had been firing warning shots at them to keep away from the border. Although this was the first incident in 2011, this year has been a terrible year in the US-Pakistan relationship, beginning with the Raymond Davis affair. Davis was a CIA contractor working under the cover of the US Embassy in Islamabad who shot two Pakistani men in January, claiming they meant to rob him. The affair highlighted the complex relationship between the two intelligence agencies, whose members distrust one another even as they work together in joint operations. Many Pakistanis complain the incident exposed problems inherent in the large US intelligence presence in their country. During his April 2011 visit to Washington, Lt Gen Ahmed Shuja Pasha, head of Pakistans Inter-Services Intelligence, asked the CIA to withdraw intelligence operatives from Pakistan and curtail its unpopular drone strikes. Mullen made clear that the UAV operations in Pakistan would continue, describing the Afghanistan-Pakistan border region as the epicentre of terrorism. The White House then ordered the May 2 attack on Osama bin Ladens compound in central Pakistan without apparently seeking Pakistani permission or notifying Pakistani authorities in advance. In response, on May 14, a joint session of both houses of Pakistans parliament unanimously enacted a resolution to defend Pakistans sovereignty, security, and territorial integrity against US military actions. Geography and other factors force Afghanistan, Pakistan, and the United States to collaborate despite their differences over the border region. But an urgent task is clearly to clarify the rules of engagement under the new conditions of a departing Western military presence, a resurgent Taliban, and a Pakistani government and military frustrated with the United States and Afghanistan, but still open to some cooperation. When President Asif Ali Zardari met Marc Grossman, the new US Special Representative for Afghanistan and Pakistan who replaced Richard Holbrooke, he said they needed clear terms of engagement in the battle against militants to avoid further damaging bilateral security ties. Zardari's office subsequently explained that, In the absence of well-defined and documented terms of engagement, wrong plugs may be pulled at the wrong times by any side that could undermine the bilateral relations. The statement added that, The president said that terms of engagement should be clearly defined and specified so that any dispute could be settled amicably. Unfortunately, theres no easy way to reconcile to these differing priorities. Afghan-Pakistan-US border tensions are likely to recur-and worsen-as Nato troops withdraw from Afghanistan. With official Afghan and US backing, ISAF will increase its pressure on Pakistani authorities to prevent the Taliban from exploiting the vacuum, and will step up its attacks along the border. Rebuilding trust between the three countries will require many years, and possibly multiple generations, to achieve. In the meantime, the current status quo of wary cooperation and mutual mistrust is likely to continue. Diplomat